Method of reclaiming vulcanized polymers by treatment with metalloid hydrides



Patented Jan. 3, 1950 *S TAT ES 2,493,518

. :aMETHGD "FQRECLAIMINGZVULCANIZED --PoLYMERs BY TREATMENT wwrrnfi-METALLOID mznamas Francis P. "*Baldwin, Woodbridge; N J .assignor toStandard 0il Developm'ent Company, a corporation of Delaware ,NoDrawing. ApplicationlAll ust' 7,,1945, .Serial No. 6099194 -8;:C.laims.

"This: invention relates to -low temperature interpolymers oflsobutylene-with a-polyolefin; 'relates particularly totherecoveryofused poly- 'mers;..and relates especially'to-the reclaim of curedpolymeruby the application thereto'ofhot hydrogen sulfide.

One of the more important substitutes for rubber is the low" temperatureinterpolymer-of isobutylene" with a; multiolefin preparedat tem-'peratures ranging from about 40 C. to 164= 0., that isattemperaturesbetween about '40 F. to '262'.4 R; by the application tothe mixed olefins of a dissolved"FriedeleCrafts catalyst as is shownindetail in'U: S. Patents Nos. 2,356,127 and 2,355,128 issued August22,1944. ';1This,p olymer cures readily with sulfur; especially inthepresencegofna' sulfurization aid suchas tetramethyl thiuram disulfide,.to yield; ,bodies Whaving tensile strengths ranging from'500 lbs; to"4500 lbs. per squarefiinch, .with 'elongationsat break ranging,iromj250%' to 1200%. Many at- .,.tempts,.havebeenmade to recover thispolymer .from.worn structures such .asitires and inner tubes,.-for.reuseand various methods have been Forthe :present invention, hydrogen.sulfide is the preferred. andv outstandingly superior ,devul- Icanization material. .However, it, is not the. only usable substance,sincehydrogen selenide andhydrogen telluride are alsooperative-However, the v-.poisonousn ess and higher. price of .both of thesecompounds render them much less satisfactory. In addition,variousof-thegaseous, inorganic hyedride -reducingragents such. asphosphine, arsine and stibine aresimilarly-useful, although in this.instance alsothe higher costandpoisonous character of thematerialsrenders them much less satisfactory. for. general -use. Accordingly,.the devulcanizingagentsof the, present invention are the. gaseous.hydrides of elements selected from ..the .6th.and {1th-columns. of..thePeriodic Table, .said ,columns being commonlyv referred to. as ..Group-V and VI. respectively.

,Thus,. ,the..invention,, applies. to a ,cured.,isovl,loutylenediolerlnpolymer, a., compound containjthe Ca-t .;.-2:dng hydrogen and sulfur, at elevated temperatures to :devulcanize.theapolymera and prepare; it i for recompoundlngc and recuring..;-'Other objects and :details i of -the invention:.-wi1 -.,be apparentfrom thefollowing description.

' The raw material .of the .presentlinvention is a. low-temperatureinterpolymer ofanrisoolefin with amultiolefin; all of :thelowerlisoolefins vandpolyolefins being broadly useful" forswtheapqlymer."The preferred:isoo'lefln- .is risobutylene but under ---certaincircumstances such 1 substances .-;as ,212- -methyl==pentene'-1}2-methyl .hexene-.1';' 2- methyl --'heptene- 1-- or -th'e like are.similarly usable. ri'llhe preferred -multiolefin is isopreneoranyaconJugated-idiolefin having 4410 6 carbonatomswper molecule such asbutadiene, piperylenerorzedimethyl: butadiene, -..but other multiolefinsshaving '-from a to-10- carbon atomssuch .as dimethallyl or myreene maybe used likewise. :1 Furthermore, cyclopentadiene may be usedeffe'ctively lnstead l of a multiolefin.

The reactants: are mixed-together in theratio of: a major proportion'of'. the -isoolefinand a min0r proportion of: the multiolefin or.ofcyclo- 25.:

pentadiene; the-preferred proportions-beingfrom to 99.5 parts by weightof the isool;efin.--with -from30-to 0.5 parts bywei'ght ofthesmultiolefin. The mixedolefins area-preferablywcooled to atemperature ranging from..S-'-40"C. tote-7165 5 C. This .may-:be-accomplished -by theuse of airefrigerating. jacket upon thereactoror a storage tankiorwthe-mixed olefinsppor mayxbei-accomplished -by-ithevuse of an internal zrefrigerant. Forthis purposesuch substances.asaliquid butane, liquid; or solid. carbon dioxide;liquidvethaneeliquid ethylene or even liquid'm'ethane arersuitable.

The polymerization is conducted by the application to the cold mixedolefinic materiahpt a Friedel Crafts catalyst selected from the ;,listgirgembvNrO: Galloway inhis article on'fffllhe Friedel-Crafts synthesisprinted the issue; of jqhemieal' Reviews published" for the AmericanChemical Society at Baltimorein "1935' in'yolume XVII, No? 3; thearticle beginning on page"32'7, ,.;the list,being particularly w-ellshownon page 375. 1 -b qflal w alumin 10W reeain irm rqqm- V te m al hri hayingeless {than 3 carbon, atoms .per; molecule is pref ed. hesneqesmgcha acte s i aofi havinasolve p wsr i tha tshMLh Ye aJ- ee .-.ing..point,,helow 0? C.,:;- thereby beingn loweezmine. al hc e i isn tneessa y hatd eiireeai s point he at or below the freezing point of thepolymerization reaction; and that it boil away from the Friedel-Craftssubstance with a nominal rise intemperatureduring the boiling of notmore than l'or 2 degrees, thereby being noncomplex-forming. With some ofthe polyoleflns,

gaseous boron trifiuoride may be used and with 7 methyl chloride or.carbon' disulfide or liquid butane,1liquid .propane, liquid ethylene,or the 1 like... Aluminum. bromide is conveniently usable liquid hexaneand the like.

- with ,hydrocarbonsolvents such as liquid propane, liquid ethane,liquid butane, liquid pentane, Also double salts of t-or complexesaluminum chloride and aluminum With boron ibromide are soluble in thesehydrocarbons and are"particularly useful. r

The'polymerization'is conveniently conducted -.by spraying the liquidcatalyst or catalyst solutionithrough .a nebulizer or spraying nozzleonto the .surface of therapidly stirred cold olefinic material- Thereaction, especially with the more active'catalysts, proceeds promptlyto yield the desired polymer.

f, This: polymer preferably has a molecular weight,as determined by theStaudinger method,

.' .or a ,Staudinger number, of from 30,000 to about "85,000, thepreferred range being from 40,000 to about 60,000. The polymer likewisepreferably 1 has an iodine number ranging from about /z to about50,:the, preferred range being between about ;1 and 20. The polymer is awhite, more or less transparent or translucent material with consid-"erable plasticity and cold flow.

.The material isreactive in a curing reaction with sulfur, especially inthe presence of a sulfurization aid such as Tuads (tetra methyl thiuramdisulfide). It is also reactive for a cure 'with such substances asparaquinone dioxime, especially-in the presence of an inorganic oxidiz-'ing agent such as 1910304.

The polymer is similarly' reactive with'the 'dinitroso compounds,

"either meta' or para A convenient recipe for compounding the polymeris:

- V 7 Parts .-Polymer e 100 Zinc oxide 0.5 to 10 Stearic acid 0.5 to? 7Carbon black 10 to 200 Sulfur e c s c 2to4 {Tuads 1 to 4 The Tuadsf andsulfur may be replaced by paraquino'ne dioxime or other dioximesubstances v "in the proportion of approximately 2 to 4 parts, or by a'dinitroso compound'in the proportion ofjfron 1 t o 4 or 5 parts; ormixtures of the various substances may be used.

The compound isconveniently prepared onthe roll mill, and the completedcompound maybe placed'in molds and cured at temperatures'rangjing f rom260? F. to 350 F. for time intervals ranging from a few minutes to 5 or6 hours,

depending upon the nature and amount of the curing component.

The resulting cured polymer will show a tensile strength within therange between .500 lbs. and 4500 lbs. per square inch, with anelongation at break ranging from 250% to 1200%, and a modulus ofelasticity (pounds pull to produce an elongation of 300%) ranging fromto 500. The polymer also shows a high resistance to oxidation by air andozone, shows a very high abrasion resistance, a very high fiexureresistance and other very valuable physical properties which make it asuperior replacement for natural rubber.

However, it is frequently desirable to refabricate the polymer,especially when it has been made into automobile tires or analogoussubstances and the structure worn out.

According to the present invention, the poly- ;mermay be reclaimedordevulcanized by a shredded into relatively small portions, and

placed in a closed container from which the air is displaced by a slowstream of hydrogen sulfide. The polymer in the container is then heatedin'the presence of the hydrogen sulfide to an elevated temperatureranging between'250 F. and

350 F., the heating being continued for from 1 to 4 or 5 hours,depending upon the tightness of cure of the original compound and theease of remilling desired. 7

The metalloid hydrides above mentioned may be used in the same mannerfor similar results; and insome instances, the inorganic elementscombine into the polymer to yield a polymer having modifiedcharacteristics which are for some purposes of considerable value.

The preferred procedureis' the use of gaseous hydrogen sulfide at an,elevated temperature 7 under atmospheric pressure. However, in someinstances, elevated pressures are desirable since this avoids thenecessity of shredding the cured polymer into small fragments. In someinstances also, liquid hydrogen sulfide may be used, provided thetemperature is kept below the critical temperature; and in this instancealso, the requirements for shreddingv are much eased. The time oftreatment varies .according to the temperature and the pressure as wellas according to the character of the curing agent, the degree of cure,and the molecular. weight of the original polymer. At high temperature,high pressure and very finely shredded polymer, the treatment may becompleted in a relatively few minutes EXAMPLE 1 A portion of polymerprepared from 97.5 parts of isobutylenewith 2.5 parts of isoprene (bothof 96% to 99% purity) which had been compounded according to the aboverecipe with sulfur and Tuads was shredded into small fragments and the,fragments placed in a, non-corrosive container. The container was closedand a slow stream of ,hydrogen sulfide passed through: The

I 12 hours.

- Batcl1 Wt the container, cooled somewhat and placed on the mill. Theywere found to be plastic and readily millable. The devulcanized polymerbanded within"2: minutes, aa'n'd' wasreadilymemilledwith additionalsulfur aandTuads. The remilled polymerwas"thenl'placedinunolds"andpured'at 307 F. for '30 minutes-toyiel'deapolymer having .an adequate tightness of cure. Test samples cut-from' the "cured "polymer showed good strength,

good elongation and.goo'd phy'sica1 properties in general; thetensilestrengthiat break being about 1800 pounds per square inch, theelongation at break being-about .l150%,; themodulus being about 350. I

.These results show' .the. qua1ity'ofreclaimed; de-

vulcanized"materialiafter-*recompouridingaandxrecuring.

EXAMPLE 2 A quantity of cured polymer was obtained which was known tohave been compounded according to the following recipe and cured:

Compound l Batch Wt 165. 0 Cure Time @300 F 30 Tensi1e-l [0d.-@300-E1ong .2390e540-700 The material"compoundedpaseabove indicated, wastreated at 1605.C.inarslowastream'ot.hydro- {This reclaim was treated at160 C. in hydrogen sulfide for two hours which was found to besufficient time to make the reclaim completely solutile win 55* "naphtha*withoutuniiling. This i ma- 5 terial at 'the end or this treatingtimers'howed-a "Mooneyviscosity' ('8'minutes"at 1-00"C:) "of-63.

A third sample of reclaim known tohave 'been compounded according to thefollowing "recipe and cured was also treated:

Compound -3 Polymer 1 100. 0 Zinc Oxide 5.0 "StearicZAcid 2. 0v-Semi-reim'orcin Furnac 50.0 'Process0i1 5. 0 Sulfur 2.0"Tributylidene-anilina 1:0

Batch Wt .165. 0 Cure Time 300-E1ong. minutes. 120 Tensile-Mod.300-Elong 2400=480740 ing subjoined table.

'Compou1id'# Polymer Stearic Acid Semrreinior'cin Furnace Black ProcessOil 1 gSulfur Tetramethylthiuram disulfide' --Mercaptobenzothiazole 4Tributylidene-aniline 5 Tensi1e-Mod. 300Elong.:

Cured l0'-/320-F. PoorGure --790-9-13l0 Oured.20'/320 .2650-5301-6901580-205-990 1340-1245-1030 Cured 4o'/320 2530-68d-620 2285-255 90023955-270-840 Cured' s a/320 F 2470-720 600 -2375-340-s10 2605-360-750Cured. 120/320 F 2375-680-630 2275-445400 1535-475 720 1 Gastex. 2 Forum40. i Tuads. Captax.

gen sulfide-for three hours,.thislengthnftime Theithree samples. ofreclaim previonsly 'treatof treating 'beings-ufii'cient to*render-theshredde'd reclaim completely soluble in'55 naphtha withoutany milling. The material afterthis treatment showed a Mooney viscosity(8 minutes at 100 C.) of 105.

Another sample of cured reclaim known to have been-compounded-according=to thefollowing recipe and cured was -also'-*s-iniilarly processed:

Compound 2 Polymer Zinc Oxide. Stearic Acid Semi-reiniorci Process OilSulfur .e ldercaptobenzothiazole ed were then separately compounded withvarying: amountslof different types of curing aids, curedfor varyinglengths or time and tested to yield the inspection recoidsshowniniT-ables 1, 2 and 3.

These results show the excellent quality of reclaim preparedaccondingitosthis process.

l Evaluatzon of reclazm 8834 1 7 Compound 1 2: 3 4", 5 6 I 7 8 Rec1aimedpolymer compound" 165.0 165.0 165.0 165.0 1650 ZinolOxide 5.0 .0 .7 5.05.0 Sulfur .0 2.0 Tettamethylthiuram disulflde 2 0 Mercaptobenzothiazole Ttibutylidene-aniline 4 Control:

Oompoundl V OompoundS TensileMod.@300-Elong.: V

Cured 10/320F 995150930' 2265-3354360 2495435-800'1610-200-9101510-185-960 2450-365-750' 2520-420-740 2350415760 Cured /320F1445-200-1030 2350-475-740 2460-590-710 2160-320-870 2110-295-8402595-575-690 2625-575-710 2585-635-690 v Cured 40/320'F 1970-265-8702420-5150420 2276-755-620 2400-435 790 2190-3185460 2530-675-6302615-730-660 2570-7104350 Cured /320 F e. 2175-325-880 2280-745-6701990-815-590 2545 520450 2320-515-730 2555-740 610 2540-7506302450775-6l0 Oured/320F 2225- 410-800 2220-615-660 2400-730-6402445:5215-6902345-575-710 2485410-620 2585-830-(530 2230-780-600 1 100parts of polymer, 65 parts of compounding ingredients. 7 I Tuads. V i VCaDtax. w 7 V r ii 808. V V

' TABLE II Evaluation of reclaim 8834-2 Compound 1 2 V 3 4 I 5 V C 6 C V7 8 Reclaimed polymer compouni Zinc Oxide Tetramethylthiuram disulfideMeroaptobenzothiazole 3 5 .iTribntylidene-aniline 4 Control: 7

v Compound 1. L.

V 7 Compound?) TensileMod.@300-Elong.: V V

Cured'10/320-F 1340-165-990 2110-375-770 2280480430 575--9301510-250-830 2270-410-800 2340-425-770 2370-480-740 Cured 20/320 .e1750-220-730 2250520-710 2210-590-700 1890245-930 1770-3l5.8302580-520-750 2430-5751410 2340-620-670 Cured 40/320 F 20503308202200-625-650 2530-700-690 2160-390-810 2440-650-660 1890-680-7002230-635-660 2420-745-640 Cured 80/320 F; 2260-430-790 2290-63043602300-680-660 2130-435-790 2040540800"2330690620 2320-690-6702430-690-690 OuIed120/320F 2100500730 2180-610-680 2280-700-6702290-515-750 1980-560-690 2100-630680 2280-630-690 2370-6375-710 1 100parts of polymer, 65.5perts of compounding ingredients. I Tuads. iOaptax. V 1 4 808.

TABLE III 1 7 Evaluation oflreclaz'm- 8834-3 Compound# 1 2 I 3 4 5 6 7 8Reclaimed polymer compound Zinc Oxide 'Sulfur- Tetramethylthiuramdisulfide Meroaptobenzothiazole 3 Y 1 r Tributylidene-aniline 4 Control:Y

Compound 1- CompoundS Tensile-Mod. 300Elong.: i

Cured 10/320F 1020-160-920 1770-340-700 220045404350 1610-200-9301180--890 2370315830 2520-405-780 2370-355-800 Cured 20/320F1760-200-920 2330-465-720 2470-630-670 2090-300-840 1860-240-8902470-425-730 2690-540-730 2610520740 Cured 40/320F 2160-275-8502650520750 2580-735-670' 2380-410-800 2050-345-780 2370-510-6802560-630-650 2550-585-710 'Cured 80/320 F-. 2410-380-820 24805657102460765-640 2380-500-730 2130-470-750 2590-680-650 2630-720-650'2480-700-670 'Cured l20/320F i. 2590-470-780 2450-580-710 2440-845-6102510-620-740 2160-505-720 235045404530 2730-735-660 ,No data 1 mil-partsof polymer, 65 parts of compounding ingredients. 1 Tnads. i Y r 3Captor. 808p V V XQ'MP Also the 'partially devulcanized material may be7 E LE 4 milled; for a substantial length of time and. then 1 the ab vmp the P y in milled into a further portion of fresh raw polyeach instand vul anized t complete u e5 mer to effect a substantial improvement inthe V ity in 55 naphtha by the hydrogen sulfide treat- 7 extruding andprocessing properties of the comment- 2 This, t is not necessary, Sincepound, since the material shows a higher bruise e ly rresults areobtainable by a resistance, less swell from the extruder and easpa a e aa n onlyy this prooedure, Y ier handling throughout the subsequentprocessa somewhat higher tensile strength material is 7 ing; and 1 ahigher g hich, for a obtained, and a material which, while it doesnotpurposes, is advantageous. V I

band on the mill as quic y and asily as the Thus the process of theinvention devuloanizes, fully devulcanized. material, yields a compoundor reclaims a cured'polymer'to yield a material haying adefinitelyhigher modulus than is :obsuitable forremilling', recompounding and.retained from the fully. devulcanized material. 75' curing toyielda newpolymer structural element.

While there are above disclosed but a limited number of embodiments ofthe process of the invention, it is possible to produce still otherembodiments without departing from the inventive concept hereindisclosed and it is therefore desired that only such limitations beimposed upon the appended claims as are stated therein.

The invention claimed is:

1. In the process for reclaiming an elastic polymer prepared by thesteps of cooling a mixture of isobutylene and a member of the classconsisting of cyclopentadiene and a multiolefin having from 4 to 10carbon atoms per molecule to a temperature within the range between -40C. and 164 0., polymerizing the cooled mixture by the applicationthereto of a Friedel- Crafts catalyst in solution in an inert organic,non-complex forming solvent which is liquid at the polymerizationtemperature and curing the resulting polymer by reaction with sulfur,the improvement comprising heating the cured elastic polymer to atemperature Within the range of 250 F. to 350 F. in the presence ofadded hydrogen sulfide until said polymer becomes plastic and millable.

2. In the process for reclaiming an elastic polymer prepared by thesteps of cooling a mixture of 70 to 99.5 parts by weight of isobutyleneand 30 to 0.5 parts by weight of a diolefin having from 4 to 6 carbonatoms per molecule to a temperature within the range between -40 C. and164 C., polymerizing the cooled mixture by the application thereto of analuminum halide catalyst in solution in an inert organic, non-complexforming solvent which is liquid at the polymerization temperature, andcuring the resulting polymer by reaction with sulfur; the improvementcomprising the step of heating the cured polymer in a closed zone to atemperature within the range of 250 F. to 350 F. for 1 to 5 hours in thepresence of hydrogen sulfide added to said zone, whereby the elasticpolymer becomes devulcanized and plastic.

3. In the process for reclaiming a polymer prepared by the steps ofcooling a mixture of a major proportion of isobutylene and a minorproportion of isoprene to a temperature within the range between 40 F.and 262.4 F., polymerizing the cooled mixture by the application theretoof an aluminum chloride catalyst in solution in an inert organic,non-complex forming solvent which is liquid at the polymerizationtemperature, and curing the resulting polymer by reaction with sulfur inthe presence of 5 to 10 parts of zinc oxide per 100 parts of polymer;the

improvement comprising the steps in combination of shredding the curedpolymer and heating it to a temperature Within the range of 250 F. to350 Fpfor 1 to 5 hours in a stream of hydrogen sulfide, and milling thepolymer to plasticity.

4. In the process for reclaiming a polymer prepared by the steps ofcooling a mixture of isobutylene and a diolefin having from 4 to 6carbon atoms per molecule to a temperature within the range between 40F. and 262.4 F., polymerizing the cooled mixture by the applicationthereto of an aluminum halide catalyst in solution in an inert organic,non-complex forming solvent which is liquid at the polymerizationtemperature, and curing the resulting polymer by reaction with sulfur;the improvement comprising the steps in combination of heating the curedpolymer to a temperature within the range of 250 F. to 350 F. in thepresence of added hydrogen sulfide for 1 to 5 hours, compounding theresulting plastic polymer with further portions of sulfur and thereafterheating the recompounded polymer to curing temperature to obtain avulcanized elastic product.

5. A process according to claim 1 wherein the polymer is prepared bypolymerizing a mixture of isobutylene and cyclopentadiene.

6. A process according to claim 2 wherein the diolefin is butadiene.

7. A process according to claim 2 wherein the catalyst is aluminumchloride in solution in an alkyl chloride having less than 3 carbonatoms per molecule.

8. A process according to claim 3 wherein the aluminum chloride catalystis in solution in methyl chloride.

FRANCIS P. BALDWIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,137,584 Ott Nov. 22, 19382,305,412 Frolich Dec. 15, 1942 2,356,128 Thomas Aug. 22, 1944 OTHERREFERENCES Baldwin (1), Ind. and Eng. Chem, Sept. 1944, pp. 791-795.

Baldwin (2), Division of Rubber Chemistry Abstracts of Papers presentedat the Spring 1944 meeting, April 1944, pp. 11Q-12Q.

1. IN THE PROCESS FOR RECLAIMING AN ELASTIC POLYMER PREPARED BY THESTEPS OF COOLING A MIXTURE OF ISOBUTYLENE AND A MEMBER OF THE CLASSCONSISTING OF CYCLOPENTADIENE AND A MULTIOLEFIN HAVING FROM 4 TO 10CARBON ATOMS PER MOLECULE TO A TEMPERATURE WITHIN THE RANGE BETWEEN-40*C; AND -164*C., POLYMERIZING THE COOLED MIXTURE BY THE APPLICATIONTHERETO OF A FRIEDELCRAFTS CATALYST IN SOLUTION IN AN INERT ORGANIC,NON-COMPLEX FORMING SOLVENT WHICH IS LIQUID AT THE POLYMERIZATIONTEMPERATURE AND CURING THE RESULTING POLYMER BY REACTION WITH SULFUR,THE IMPROVEMENT COMPRISING HEATING THE CURED ELASTIC POLYMER TO ATEMPERATURE WITHIN THE RANGE OF 250*F. TO 350*F. IN THE PRESENCE OFADDED HYDROGEN SULFIDE UNTIL SAID POLYMER BECOMES PLASTIC AND MILLABLE.